Methyl Ester Sulfonate (“MES”) surfactants are currently used in many applications including laundry detergents and may be produced from renewable resources such as palm oil or coconut oil. In recent years as the price of petrochemicals has increased, these renewable resource surfactants have become a more attractive option for inclusion in certain laundry detergent formulas. The process for the production of MES is well known and established (See, for example, U.S. Pat. Nos. 5,587,500; 5,723,533; and 6,058,623 to The Chemithon Corporation). Generally speaking, natural oils (or triglycerides) are chemically converted to methyl esters and glycerol. The methyl esters are then sulfonated on the alpha-position, which is followed by a digestion step to ensure optimal conversion to the desired alpha-sulfonated methyl ester sulfonate molecule. After the digestion step, the material is typically bleached and neutralized, and these two steps can be done in either order according to certain processes known in the art.
Various by-products may be formed during the MES process, and each can have an impact on the overall performance and stability of the MES in the finished detergent formula. One such by-product is commonly referred to as “di-salt”, and can be described as the neutralized form of the desired MES molecule (sulfonated and neutralized on the alpha position) that has also had the methyl portion of the ester neutralized with another cation. This di-salt molecule has different properties than the equivalent MES molecule, and can give rise to certain performance and stability issues. For this reason, most MES processes attempt to minimize the level of di-salt that is formed during the process (typically the standard is less than about 10%). This is typically accomplished by tightly controlling the neutralization step to avoid areas of high pH, and also by minimizing the level of water that is present prior to neutralization.
This minimization of di-salt level requires processing investments, and thus the price of MES material with low di-salt level is generally higher than an MES with higher di-salt level. In the past, because di-salt has been perceived as an undesirable material that can negatively impact cleaning performance and stability, this extra cost has been accepted.
Therefore, a need exists to develop reduced cost laundry detergent compositions that have both good cleaning performance and stability that can utilize the less-expensive MES having a higher level of di-salt.